It has been estimated that 60% of all runners will, at some time, sustain an injury that will prevent them from running. Numerous studies have attempted to document the etiologic factors associated with certain running related injuries; however, many of these studies are based on expert opinion or are descriptive studies which failed to utilize a control group. While this information is useful, there is a clear need to establish whether a certain combination of biomechanical, anthropometric, and training variables is related to specific running injuries. The purpose of this study is to extend our knowledge of running related injuries by determining whether relationships exist between selected biomechanical, anthropometric, and training variables and runners afflicted with one of the following injuries: iliotibial band friction syndrome, patellofemoral pain syndrome, posterior tibial syndrome (posterior shin splints), achilles tendinitis, and plantar fascitis. Specifically, the objectives of this study are: 1) to examine differences between a non-injured cohort of runners and five cohorts of injured runners according to selected biomechanical, anthropometric, and training measures, 2) to explore multivariable relationships among these measures in both well and injured cohorts, and 3) to develop a specific hypotheses concerning risk factors for injury that will be later tested in a prospective controlled clinical trial. Injuries to the knee, shin, achilles tendon, and foot comprise over 80% of all reported running injuries with the aforementioned injuries frequently cited as the most common. Recreational and competitive runners who have been running a minimum of 10 miles/wk for at least 1 yr. will undergo biomechanical, anthropometric, and orthopedic evaluations and complete a runner's history form. Thirty-five subjects per injury group and an equal number of non-injured control subjects will be tested each year (total of 105 subjects per group over 3 yrs). the biomechanical analysis will include obtaining rearfoot movement data (maximum pronation, etc) from high speed (200 fps) film and kinetic data (ground reaction forces, center of pressure, etc) from a force platform while subjects run along a 247 m instrumented runway. Lower extremity strength will be assessed using a Biodex isokinetic machine. The anthropometric measurements will include: arch index, leg lengths, ankle flexibility, Q angle, assessment of lower extremity and back alignment, and dynamic foot angles. Training variables will be obtained from the runner's history form. Multivariable analyses of pairwise differences between the injury and control cohorts will be performed using stepwise discriminant analysis and classification and regression tree analysis.